Previous studies have identified two subsets of essential hypertensives, those whose blood pressure increased when sodium intake was increased from 9 to 249 mEq/day (salt-sensitive) and those whose blood pressure did not change (salt-resistant). The salt-sensitive patients also showed more sodium retention and weight gain before coming into sodium balance than did the salt resistant. In preliminary studies of calcium and magnesium metabolism salt-sensitive hypertension, an increase in sodium intake from 9 to 249 mEq/day was associated with an increase in urinary calcium from 8.5 to 19.3 mEq/day whereas urinary magnesium showed little change (7.4 versus 8.4 mEq/day). These findings suggest that the greater sodium retention in the salt-sensitive hypertensives may be associated with an increase in calcium excretion. The role of calcium loss in the associated rise in blood pressure remains to be determined.